A clown bastard child is a child who was possibly switched out at birth by entities unknown (clown bastard aliens)...possibly as a joke on the unsuspecting parents. Parents may leave the hospital with what they perceive to be the most sweetest child in the world...only to discover about 5 years later that the child's behavior is so atrocious it makes the parent proclaim that the child could not possibly be theirs because of how said child acts. The parents were fooled because the child resembles them but his actions later in life may prove otherwise. These children are often spawned...not born
Clown- because it seems a joke was played on you.
Bastard- because this child surely CANNOT be yours!